Multi-layered optical disk with shifted track and layer identification and method of detecting a track

ABSTRACT

A multi-layered optical disk comprising a plurality of recording layers accumulated in the thickness direction wherein a light beam is focused on one of tracks of one of the layers thereby to record and reproduce data, the optical disk being characterized in that recording layers each have an identification section storing an address of the recording layer which the identification section belongs to.

This is a divisional application of U.S. Ser. No. 09/245,196, filed onFeb. 5, 1999 (U.S. Pat. No. 6,421,315), which is a divisionalapplication of U.S. Ser. No. 08/917,995, filed on Aug. 25, 1997 (U.S.Pat. No. 5,870,374), which is a division of U.S. Ser. No. 08/493,929,filed on Jun. 23, 1995 (abandoned), which is a division of U.S. Ser. No.08/180,845, filed Jan. 12, 1994, issued as U.S. Pat. No. 5,428,597 onJun. 27, 1995, which is a division of U.S. Ser. No. 07/595,422, filedOct. 11, 1990, issued as U.S. Pat. No. 5,303,225 on Apr. 12, 1994.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to an optical disk used for data recording andreproduction, especially to a multi-layered optical disk having multiplerecording layers.

(2) Description of the Prior Art

In recent years, this type of optical disks have been developed activelydue to the large memory capacity and high access speed. An optical diskshown in FIG. 1 has been proposed in order to further increase thememory capacity.

This optical disk 12 comprises three recording layers 8 a through 8 cformed of a photochromic material such as spyropyrene, the layers beinginterposed between a pair of bases 13. The recording layers 8 a through8 c have sensitivity peaks in wavelengths λ₁ through λ₃ (FIG. 2),respectively while allowing lights having the other wavelengths totransmit therethrough.

Data recording and reproduction is done in the following way. A light isemitted from a light source 9, such as a laser, which varieswavelengths, and focused into an extra fine light beam by a focusingoptical system 10, thereafter the light is illuminated on the disk 12.The light is transmitted through the recording layers 8 a, 8 b and 8 cand is detected by a light detector 11 provided on the other side fromthe light source 9.

Data recording will be described in more detail. If the light emittedfrom the light source 9 and illuminated on the disk 12 has a wavelengthλ₂, it is transmitted through the recording layers 8 a and 8 c but isabsorbed into the recording layer 8 b, whereby a data is recorded in thelayer 8 b.

For data reproduction, only the data recorded in the layer 8 b can beretrieved by illuminating a light of λ₂.

As apparent from the above, memory capacity is increased by providingmore recording layers.

However, providing more recording layers enlarges the total thickness ofthe recording layers. In order to record and reproduce data in such athick disk only by use of wavelength difference without detecting exactpositions of the layers, the light beam should have quite a largediameter, which prevents high density recording.

Also, the large light beam diameter causes crosstalks betweenneighboring tracks.

SUMMARY OF THE INVENTION

Accordingly, the present invention has an object of offering amulti-layered optical disk which detects an exact position of eachrecording layer for minimizing the diameter of the light beam and thusremarkably enhancing the recording density.

This invention has another object of offering a multi-layered opticaldisk which prevents crosstalks between neighboring tracks and layers.

The above objects are fulfilled by a multi-layered optical diskcomprising a plurality of recording layers accumulated in the thicknessdirection wherein a light beam is focused on one of tracks of one of thelayers thereby to record and reproduce data, the optical disk beingcharacterized in that recording layers each have an identificationsection storing an address of the recording layer which theidentification section belongs to.

The identification section may store an address of the track which theidentification section belongs to.

The tracks of two of the layers neighboring in the thickness directionmay be shifted against each other in the radial direction by half of atrack pitch.

The optical disk may have two recording layers.

The tracks each may comprise a plurality of sectors.

The sectors each may have an identification section, which storesaddresses of the recording layer, the track and the sector which theidentification section belongs to.

The identification sections may be shifted against one another in thetracking direction.

The above objects are also fulfilled by a multi-layered optical diskcomprising a plurality of recording layers each having a plurality oftracks, wherein the layers are accumulated in the way that the tracksare aligned in the thickness direction; the optical disk beingcharacterized in that at least one of recording layers has a firstidentification section storing an address of the tracks which arealigned in the thickness direction and one of which has the firstidentification section; and that the recording layers each have a secondidentification section storing an address of the recording layer whichthe second identification section belongs to.

The first identification section may have long enough a pit to allow arecorded data to be reproduced if the light beam is focused on eitherone of the recording layers while the second identification section hasshort enough a pit to allow the recorded data to be reproduced if thelight beam is focused on the layer specified.

The tracks each may comprise a plurality of sectors, each of which hasits address stored in the first identification sections

The above objects are also fulfilled by a multi-layered optical diskcomprising a plurality of recording layers each having a plurality oftracks, wherein the layers are accumulated in the way that the tracksare aligned in the thickness direction; the optical disk beingcharacterized in that at least one of recording layers has a firstidentification section storing an address of the tracks which arealigned in the thickness direction and one of which has the firstidentification section; and that the recording layers each have a secondidentification section storing an address of the recording layer whichthe second identification section belongs to, the second identificationsections being shifted against one another in the tracking direction.

In the above construction, since each layer of the optical disk has itsown address stored in the identification section thereof, the exactposition of the desired recording layer is easily found. As a result,the diameter of the light beam can be minimized, realizing high densityrecording.

Moreover, when the identification sections of the layers neighboring inthe thickness direction are provided so that the light beam may not befocused on two or more of the sections simultaneously, crosstalksbetween neighboring identification sections can be substantiallyprohibited. Therefore, the desired identification section, namely, thedesired recording layer, can be accurately detected.

In conclusion, the above construction provides high precision, highdensity recording on multiple layers of an optical disk.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent form the following description thereof taken inconjunction with the accompanying drawings which illustrate specificembodiments of the invention. In the drawings:

FIG. 1 is a view showing a construction of a conventional multi-layeredoptical disk along with a data recording and reproduction apparatus;

FIG. 2 is a view showing a wavelength spectrum recorded on the aboveoptical disk;

FIG. 3 is a vertical cross sectional view of a multi-layered opticaldisk as a first embodiment of this invention;

FIG. 4 is a plan view of the optical disk of FIG. 3;

FIG. 5 is a view showing a construction of an identification section ofthe optical disk of FIG. 3;

FIG. 6 is a vertical cross sectional view of a multi-layered opticaldisk as a second embodiment of this invention;

FIG. 7 is a plan view of the optical disk of FIG. 6;

FIG. 8 is a vertical cross sectional view of a multi-layered opticaldisk as a third embodiment of this invention;

FIG. 9 is an enlarged view of one track of FIG. 8; and

FIG. 10 is a vertical cross sectional view of a multi-layered opticaldisk as a fourth embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment I

A first embodiment of this invention will be described referring toFIGS. 3 through 5.

As shown in FIG. 3, a multi-layered optical disk 1 comprises upper andlower base plates 2 opposed to each other, a first recording layer 3superposed on a lower surface of the upper base plate 2, a secondrecording layer 4 superposed on an upper surface of the lower base plate2 and a spacer 5 made of UV resin for prohibiting the recording layers 3and 4 from contacting each other. The layers 3 and 4 have known pitconstructions.

As shown in FIG. 4, the recording layers 3 and 4 comprise a plurality ofconcentric tracks 6 a and 6 b, respectively (the tracks are shown inparallel for convenience in FIG. 4). The tracks 6 a and 6 b are shiftedagainst each other in the radial direction by half of a track pitch Pt.Each track is divided into a plurality of sectors S, each of which hasan identification section (referred to as ID_(a) for the track 6 a andas ID_(b) for the track 6 b) and a data field DF for storing data. Asshown in FIG. 5, each identification section ID_(a) or ID_(b) comprisesa section SYNC for synchronizing clocks, an address mark AM indicating astart of an address signal, a track address TA, a sector address SA anda recording layer address LA.

The multi-layered optical disk 1 is produced by forming the recordinglayers 3 and 4 on the base plates 2 having projecting portions and thenadhering the base plates 2 with an adhesive made of UV resin (theadhesive is solidified into the spacer 5). The spacer 5 is desirably asthin as possible but a thickness of 10 to 100 μm is acceptable. Theprojecting portions allow the layers 3 and 4 each to have the known pitconstruction.

A data is recorded in the multi-layered optical disk 1 in the followingway. First, a desired recording layer 3 or 4 is retrieved by reproducingthe recording layer addresses LA of the disk 1. Second, a desired track6 a or 6 b is retrieved by reproducing the track addresses TA of theretrieved layer. Third, a desired sector S is retrieved by reproducingthe sector addresses SA of the retrieved track. Finally, a data isrecorded in the data field DF of the retrieved sector S.

If a layer whose address is reproduced is not the desired one in theabove first retrieval, the following operation is carried out toretrieve the desired one. The light beam is defocused and illuminated onthe disk 1 while changing the position of the focus. Each time the lightbeam is transmitted through the layers 3 or 4, an S curve is formed toindicate a focusing error. The zero cross point of each S curve isdetected until the same number of zero cross points as the ordinalnumber of the desired layer is detected. The ordinary number isdetermined as follows: when the layer 4 is the reference layer, thelayer 4 is the first layer and the layer 3 is the second layer. When theabove number of zero cross points are detected, namely, when the desiredlayer is retrieved, the light beam is focused again and theidentification section IDor ID_(b) is read out for confirming that thedesired layer is retrieved.

The desired track TA₁ is retrieved in the following manner. When a trackaddress TA₂ is reproduced, the position of TA₂ is compared with theposition of the desired track address TA₂, and the head of the lightbeam is moved by a linear motor until it reaches the desired trackaddress TA₁ (rough retrieval). If the desired track address TA₁ isconfirmed, the operation advances to the next: step of retrieving thedesired sector S. If not, all the track addresses TA₂ are reproduced oneby one by the tracking actuator until the head reaches the desired trackaddress TA₁ (fine retrieval).

The desired sector S is retrieved by comparing the desired sectoraddress SA₁ and a read address and by rotating the optical disk 1 untilthe head reaches the desired sector address SA₁.

Data reproduction is done in the same manner as data recording.

Since the recording layers 3 and 4 comprise identification sectionsID_(a) and ID_(b), respectively, having the recording layer addresses LAin this embodiment, whichever layer the light beam is focused andtracking on can be accurately detected. Even if the number of recordinglayers are increased to enlarge the total thickness of the layers,highly precise recording and reproduction is realized with high density.Providing a track address TA in each identification section allows easyconfirmation of the desired track.

Moreover, the tracks 6 a and 6 b are shifted against each other in theradial direction by half of the track pitch Pt. Practically speaking,therefore, the light beam is never illuminated on the adjacent recordinglayer, greatly preventing crosstalks between neighboring identificationsections and between neighboring data fields.

Embodiment II

The second embodiment of this invention will be described referring toFIGS. 6 and 7. The same elements share the same numerals with EmbodimentI and their explanation will be omitted.

This embodiment is distinct from Embodiment I in that the identificationsections ID_(a) and ID_(b) are a little shifted against each other inthe tracking direction. Desirably, the identifications ID_(a) and ID_(b)are not overlapped when seen in the radial direction.

In addition to the advantages of Embodiment I, this construction furtherprevents the light beam from illuminating neighboring identificationsections simultaneously and thus further restricting crosstalks.

Embodiment III

A third embodiment of this invention will be described referring toFIGS. 8 and 9.

As shown in FIG. 8, the optical disk 1 comprises three recording layers7 a through 7 c. The layers 7 a through 7 c have identification sectionsID_(L1), ID_(L2) and ID_(L3), respectively. The layer 7 c also hastrack/sector identification sections ID_(TS), by which tracks andsectors are identified. The tracks of the layers 7 a through 7 c are notshifted but are aligned in the thickness direction. Each track/sectoridentification section ID_(TS) identifies a group of tracks and sectorswhich are aligned in the thickness direction. The layers 7 a through 7 ceach have the known pit construction.

As shown in FIG. 9, the track/sector identification section ID_(TS) hasa pit pitch P₁, the identification sections ID_(L1), ID_(L2) and ID_(L3)each have a pit pitch P₂, and the data field DF has a pit pitch P₃, thepit pitches having the relationship P₁>P₂=P₃. Practically, P₁ is set sothat the recorded data may be reproduced well enough if the light beamis focused on either one of the layers 7 a, 7 b and 7 c (for example, P₁is 5 μm or less). P₂ and P₃ are set so that the recorded data isreproduced well enough when the light beam is focused on the specifiedlayer 7 a, 7 b or 7 c (for example, P₂ and P₃ are each 0.8 μm). In otherwords, the track/sector identification section ID_(TS) can be read outif only the light beam is focused on either one of the layers while theidentification sections ID_(L1), ID_(L2) and ID_(L3) can be read out ifthe light beam is focused on the specified layer.

How to access each layer, for example, the recording layer 7 a, will bedescribed hereinafter. In this embodiment, the layer 7 c is thereference layer and the ordinal number of the layer 7 a is known.

A light beam is focused on the layer 7 c when a specified number of zerocross points of the S curves as focusing error signals are detected, andthe identification section ID_(L3) is read out to confirm that the lightbeam is focused on the layer 7 c. Then, when a certain number of zerocross points are detected, the light beam is focused on the layer 7 a.The certain number is obtained by subtracting one from the ordinalnumber of the layer 7 a. The identification section ID_(L1) is detectedto confirm that the light beam is focused on the layer 7 a. Thereafter,the track/sector identification sections ID_(TS) are detected one by oneuntil the desired track and then the desired sector are retrieved.

In the above construction, no other signal is recorded in any portion ofthe layers 7 a and 7 b, the portion being perpendicularly opposed to thetrack/sector identification section ID_(TS); and the identificationsections ID_(L1), ID_(L2) and ID_(L3) have too small pit pitches to readout unless the light beam is focused on the desired layer. Therefore,this embodiment greatly prevents crosstalks in addition to having theadvantages of Embodiment I. Moreover, since the tracks of differentlayers are not required to shifted against one another by half the trackpitch, productivity of the optical disks is increased.

Embodiment IV

A fourth embodiment of this invention will be described referring toFIG. 10. The same elements share the same numerals with Embodiment IIIand their explanation will be omitted.

This embodiment is distinct from Embodiment III in that theidentification sections ID_(L1), ID_(L2) and ID_(L3) are a littleshifted against one another in the tracking direction. Practically, theidentification sections ID_(L1), ID_(L2) and ID_(L3) are off from thetrack/sector identification section ID_(TS) by distances T₁, T₂ and T₃,respectively. Desirably, T₁ minus T₂ or T₂ minus T₃ is the same orlarger than a length of ID_(L1), ID_(L2) and ID_(L3) each in thetracking direction. Since the identification sections ID_(L1), ID_(L2)and ID_(L3) have the same pit constructions as those of Embodiment III,the track/sector identification section ID_(TS) can be read out if onlythe light beam is focused on either one of the layers while theidentification sections ID_(L1), ID_(L2) and ID_(L3) can be read out ifthe light beam is focused on the specified layer. The layer 7 a can beaccessed in the same manner in Embodiment III.

In this embodiment, since the identification sections ID_(L1), ID_(L2)and ID_(L3) are shifted against one another in the tracking direction,the light beam is prevented from illuminating neighboring identificationsections simultaneously. As a result, this embodiment further restrictscrosstalks in addition to having the advantages of Embodiment III.

Although the tracks comprise sectors in the above four embodiments, datamay be recorded all along the tracks.

In the above embodiments, the recording layers have sensitivity peaks indifferent wavelengths. However, the disk may comprise layers formed ofan usual optomagnetic material such as TbFeCo or a phase change materialsuch as GeSbTe.

Although the present invention has been fully described by way ofembodiments with references to the accompanying drawings, it is to benoted that various changes and modifications will be apparent to thoseskilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

What is claimed is:
 1. A multi-layered optical disks comprising aplurality of recording layers each having a plurality of tracks, whereinthe layers are accumulated in the way that the tracks are aligned in thethickness direction; the optical disk being characterized in that atleast one of recording layers has a first identification section storingan address of the tracks which are aligned in the thickness directionand one of which has the first identification section; and that therecording layers each have a second identification section storing anaddress of the recording layer which the second identification sectionbelongs to, the second identification sections being shifted against oneanother in the tracking direction.
 2. A multi-layered optical disk ofclaim 1, wherein the first identification section has long enough a pitto allow a recorded data to be reproduced if the light beam is focusedon either one of the recording layers while the second identificationsection has short enough a pit to allow the recorded data to bereproduced if the light beam is focused on the layer specified.
 3. Amulti-layered optical disk of claim 1, wherein the tracks each comprisea plurality of sectors, each of which has its address stored in thefirst identification section.
 4. A multi-layered optical diskcomprising: a plurality of recording layers stacked upon each other,each recording layer having tracks for recording data; andidentification sections for identifying tracks and recording layers onwhich identification data is recorded and reproduced by focusing a lightbeam on one of a plurality of recording layers, the identificationsections of recording layers adjacent each other in a radial directionof the tracks are shifted relative to the identification section of therecording layers in a tracking direction.
 5. The multi-layered opticaldisk according to claim 4, wherein each layer is spaced from the otherrecording layer by a transparent ultraviolet hardening resin having athickness of 10 to 100 μm disposed between the recording layers.
 6. Themulti-layered optical disk according to claim 4, wherein a firstidentification section has a pit of sufficient length to allow recordeddata to be reproduced, if a light beam is focused on either one of therecording layers, while a second identification section has a pit ofsufficient length to allow the recorded data to be reproduced only ifthe light beam is focused on the recording layer specified.
 7. Themulti-layered optical disk according to claim 4, wherein respectivefirst and second recording layer tracks are relatively offset from eachother in a radial direction by half of a track pitch.
 8. Themulti-layered optical disk according to claim 4, wherein each track hasa plurality of sectors and each sector has an identification sectionwhich stores addresses of the recording layer, the track and the sectorwhich the identification section belongs to.